Modern gas filling systems or the process of filling natural gas fueled vehicles are performed by one of two methods, the fast fill or the time fill.
The fast fill process is similar to conventional gasoline or Diesel filling processes in that the vehicle pulls up to a compressed natural gas (CNG) dispenser, the filling nozzle is connected to the fill port and the vehicle CNG tank is filled rapidly as possible from the CNG system storage tanks, the CNG compressor or a combination of both. The filling process is as rapid as the CNG tank and compressor system can deliver. To achieve a full tank of CNG, the tank is typically overfilled to compensate for the heat of compression that occurs during the rapid or fast filling process.
The time fill process consists of connecting one or more vehicles to a common CNG system. The check valve in the vehicle CNG tank prevents gas outflow from the tank and only allows flow to the tank. However, as multiple vehicles are connected, the lowest pressure tank fills first as the CNG compressor builds pressure.
The compressed natural gas slow or time fill post system is typically configured with a steel tube or support structure with the CNG conveyance tubing and valves attached to the support structure.